Making porous material



Patented July 4, 1933 UNITED STATES PATENT OFFICE HANS M17813, BITTER'FELD, GERMANY, ASSIGNOR TO I. G. FARBENINDUSTRIE AKTIENGESELLSCHAFT, OF FRANKFORT-ON-THE-MAIN, GERMANY MAKING POROUS MATERIAL N0 Drawing. Application filed July 22, 1931, Serial No. 552,551, and in Germany July 29, I930.

The present invention is concerned with improvements in making porous material from molten slags, particularly for building purposes.

According to a known process a porous material having a low Weight per unit of volume is produced by running molten silicate slags, such as blast furnace slags, into water, or treating them with steam, or by admixing gas-generating substances, such as carbonates, ferric oxide, loam, moist sand etc. with such molten slags; However, the products thus obtained are generally not uniform with respect to weight by unit of volume and to strength, both being particularly dependent upon the actual conditions of treatment. When, for instance, molten slags are poured on a water sheet, a product of extremely low weight by unit of volume is obtained which, however, displays practically. no strength and rigidity whatever, and which, owing to its peculiar porous structure, avidly imbibes water by multiple quantities .of its own weight. When employing such 2. porous substances for building purposes, by

admixing a cementing material so as to obtain concrete, the quantities of heavy weight binder required are such that the advantages of employing a low weight building material are ractically forfeited, quite apart from the act that thestructures are, owing to the water-imbibing capacity of the building material, by no means. safe against the effects of frost. It has therefore been attempted to improve the qualities of such porous products by passing the slag, which immediately following the treatment with water is still viscous, through a water-cooled rolling device, with a view of causing the formation of pores predominant- 1y consisting of closed spaces (comp. Stahl &Eisen, 1923, page 1219 and if.) This method, however, necessitates the employment of special devices whose operation and maintenan'ce involves heavy expenses. 7 It has further been proposed to obtain a granular material of small grain size or loose, voluminous crumbs by pouring molten bedding of highly porous sand or similar mebeddings of equal size and equal depth (50.

slags, particularly blast furnace slags, on a terial which is heavily soaked with water. The crumbs thus obtained have been recommended for the making of low weight bricks by addition of suitable binders.

In contradistinction to such proposals, the object of the present invention is to produce, I by a simple and economical process, a porous material which is not liable to crumble on cooling, having mostly closed spaces and having, as such, a high strength.

According to the invention, a layer of modcrate thickness of molten slag is formed on a finely porous bedding preferably consisting of sand, which has been moistened with water prior to the pouring of the slag. Care should as be taken to prevent the steam, evolved in the bedding on pouring, from escaping downwardly or laterally, the aim being that the sfeam is caused to penetrate into the molten s ag.

In contradistinction to the process, above referred to, of making porous crumbs of slag by pouring the molten slag on a sand-bedding soaked with water, the process according to the invention requires a much smaller water content of the bedding. Experiments have shown that in order to obtain a porous material having high strength and closed pores according'to the invention, it is strictly preconditional to'cause the water to be imbibed by the porous bedding of sand etc. in such a. manner that only ver little water, if any at all, is visible as a s eet on the surface of the porous bedding. In contradistinction, the quantity of water required for the mak- 85 ing ofgranulated slags or porous crumbs having no strength whatever and open pores, as above described, is substantially larger I and, furthermore, not equally strictly limited, so that the porous bedding is not only soaked with water, but that a continuous water sheet having an appreciable depth is invariably formed on the top of the bedding. By way of example, when employing sand cms.), and pouring the molten slag into layers of equal thickness (35 cms.) in both cases, it is necessary to employ about 750-1300 ltrs. of water for every 1000 kgs. of slag so as to obtain a coherent material having a high mo strength and predominantly closed pores, according to the present invention whereas at least about 2000 ltrs. of water are required so as to give rise to the formation of porous crumbs, according to the known process.

It follows from these comparative tests that the presence of a continuous water-sheet on the surface of the bedding has a decisive and distinctive effect upon the nature and the quality of the porous product formed, and further, that the present process is clearly and fundamentally distinguished from the known process, also employing a bedding of moist sand, by the proportion of water to slag employed.

The weight per unit of volume of the porous slags obtained by the present invention ranges between about .5 and .75, whereas the ratio specific weight: weight per unit of volume, representing the comparative porosity, ranges between about .72 and .80. The majority of the pores in the slag are closed, the percentage of open pores only amounting to betwen about 6 and percent of the total volume of the pores.

,Ewample In a shallow pit, a stratum of slag, or battered loam, or the like which is impermeable to water, is formed. On the top of this, a layer of sand of about to cms. thickness is prepared and thoroughly soaked with water up to the surface. Upon this bedding, molten slag, such as silicate slag from a phosphorous furnace is quickly run to a depth of about 30 cms., which is uniformly swelled by the steam evolved from the bedding during solidification, the latter taking place comparatively rapidly. The solidified product breaks up into large pieces which are taken out of the pit and according to the purpose in view are worked up into suitable grain sizes in the known manner.

I claim:

1. A process of making porous material having a high strength and mostly closed pores from molten refractory slags which comprises causing the molten slag to flow on to a porous bedding soaked with water in such a manner that the level of the water is approximately equal to but not below the level of the bedding.

2. A process of making porous material having a high strength and mostly closed pores from molten refractory slags which comprises causing the molten slag to flow on to a porous bedding of sand soaked with water in such a manner that the level of the water is approximately equal to but not below the level of the bedding.

3. A process of making porous material having a high strength and mostly closed pores from molten refractory slags which comprises causing molten phosphorus furhaving a high strength and mostly closed Y HANS KRAUSE. 

